GIMP is open source and free. I don't know that it is any better than PS, but it isn't difficult and there is lots of help available, both in form of a manual and people to answer questions. Of course, these days, you can just ask Google.
A quick search shows that you can go to the chrome web store and get it on rollApp. It's a powerful editor but I don't know much about how well it will operate on chromebook. Worth a shot, I guess.
THAT FACE YOU MAKE WHEN YOU TRY TO ACCESS PHOTOSHOP, BUT EVERY TIME YOU ADD A NEW PHOTO IN, YOUR COMPUTER SHUTS DOWN; I WISH THERE WAS AN EASIER WAY TO MAKE POPULAR MEMES...